This invention relates to universal joints and more particularly to universal joints which provide a substantially constant velocity transfer of rotary motion.
Many types and designs of substantially constant velocity universal joints are well known. However, the majority of these designs are not satisfactory from a cost, production and/or serviceability standpoint and many contain rather complex means for providing constant velocity.
The universal joint design disclosed in U.S. Pat. No. 3,332,256 issued to Phillip J. Mazziotti and assigned to the assignee of the present invention, alleviates many of these problems. The aforementioned patent to Mazziotti discloses a universal joint having four equally circumferentially spaced rollers which collectively transmit torque from an inner rotatable member to an outer rotatable member. Each roller has a pilot means rotatable and pivotable within a generally elliptical bore in a groove in the inner rotatable member. Each roller also has an inner portion rotatably positioned in an axially extending groove in the inner rotatable member and an outer portion rotatably positioned in an axially extending groove in the outer rotatable member. When the joint telescopes, or when the rotatable members are disposed at an angle relative to each other and the joint is rotated, the outer portion of each roller oscillates axially within its respective groove in the outer rotatable member. In this design the geometry and cooperation of the various components of the joint are relied upon to achieve a substantially constant velocity transfer of rotary motion.
The geometry of the previously described universal joint has succeeded to a great extent in coordinating the components thereof. However, it has been found that the efficiency of the joint may be diminished by internal forces such as friction and/or binding between the components of the joint. For example, friction between the pilot means and its associated bore and between the inner portion of the roller and the groove in the inner rotatable member will oppose rotation of the rollers, thereby opposing telescoping rotating of the joint. As a result, the rollers have a tendency to slide axially rather than roll within the grooves of the outer member. This sliding creates additional friction between the outer surface of the rollers and the sides of the grooves in the outer rotatable member in which they axially oscillate.
Another problem encountered in the operation of a universal joint of the aforementioned design is binding of the torque transmitting rollers. It is desirable for smooth operation of the joint to maintain minimum machining tolerances of the joint components. This assures a smooth transfer of torque through the joint. However, the close tolerances can create problems with respect to alignment and cooperation of the roller carrying grooves of the inner and outer members. Index error between the grooves may lead to a binding of the rollers during the rotation of the joint. For example, consider the aforementioned universal joint design in which the inner and outer members each have four grooves nominally circumferentially spaced 90.degree. from each other. Also consider that one of the grooves in the inner member, due to a small machining error, is out of position with respect to the other grooves, by 0.1.degree., such that is is spaced 89.9.degree. and 90.1.degree. , respectively, from the next adjacent grooves. During operation of this joint, the rollers may bind because the inner member cannot center itself within the outer member. Furthermore, the inner member cannot assume a position of equal load distribution between the rollers. As a result, the rollers will fight or oppose each other during rotation of the joint, creating a situation in which the rollers may bind against either the inner or outer member. Misalignment of the grooves may cause similar problems.
It should also be noted that the aforementioned design does not produce a truly "constant velocity" for all angles between the two rotatable members, as is described in detail in U.S. Pat. No. 3,332,256. As explained in that patent, the four rollers cannot always be disposed on the "bisecting plane" between the inner and outer rotatable members. As the joint rotates, the rollers will be disposed at locations unequally spaced from the bisecting plane and will carry unequal loads. Again, the rollers therefore inherently tend to oppose or fight the internal movement of each other, resulting in reduced effeciency of the joint.
In practice, to reduce the efficiency losses due to internal friction and binding of the universal joint components, additional internal clearances between the components have been provided in the joint. This has not proved to be an entirely satisfactory solution. Oversized clearances can cause a chattering or clattering of the rollers against the other joint components. This chattering is due in part from the inertial loading of the components as the joint rotates. Inertial loading may result in erradic operation of the joint and may cause a more rapid wear of the joint components.